It is commonly necessary to pump liquid from a surface in the event of a flood or spill, or from the bottom surface of a tank or containment area to remove the fluid.
Submersible sump pumps are available which sit flat on the surface and can pump down to a relatively low liquid surface level. However these are generally of low capacity and are unsuitable in situations where large volumes of liquid are to be pumped.
A larger volume of flow can be generated using a remote pump with an intake line leading to the surface. Typically such pumps are provided with a generally conical strainer device that fits on the end of the suction line to prevent debris from entering the pump suction. The problem with the strainer device is that it does not allow the pump to pump the fluid level down to the floor. The pump loses suction leaving a significant standing fluid level.
It is desirable to pump the fluid level down as much as possible before losing suction.
The movement of fluid while pumping is caused by creating a pressure differential so that the fluid flows from higher to lower pressure. Because of the design of the strainer, the pump loses suction while there is still a significant amount of water to be pumped from a flat surface. This effect takes place because air breaks through into the pump suction as the fluid level drops, due to the design of the strainer device. This also happens when pumping without the strainer device.